Modulation of electrical waves



sept. 9 A1924.' 1,507,913

A. L. FITCH MODULAT I ON OF ELEGTR I CAL` WAVES Filed Aug. 29 1919 'byMMA ffy.

Patented Sept. 9, 1924.

UNITED 4STATES 1,507,913 PATENT OFFICE.

ALBERT L. FITCH, or nUTHEnEoED, NEW JERSEY, AssIGNoETo wEsTEnNELEcTmcCOMPANY, INCORPORATED, or NEW Yonx, N. Y., a conroaATroN E NEW Yonx.

MonULATIoN or ELEcTEIcAi. waves.

Application led August 29, 1919. Serial No. 820,548.

To all whom it mayvconce'm: v

Be it known that I, ALBERT L. FITCH, a citizen of the United States,residin at Rutherford, in the-county of Bergen, tate of New Jersey, haveinvented certain new and useful Improvements in Modulation of ElectricalWaves, of which the following is a full, clear, concise, and exactdescription.

This invention relates to signaling systems, and especially tomodulating systemswherein rectifying or unsymmetrically conductingdevices are used for the production of modulated high frequency waves.

Au object of the invention is to provide xueaus for producing modulatedwaves wlicrcin are associated a plurality of unsynunetrically conductingdevices in such a manner as to produce efficient modulating action. Y

A further object is the provision of a circuit arrangement of this kindincluding two-electrode discharge devices and capable of functioningwithout the space current sources which are usually provided for suchdevices'.

Still further features of the invention relate to certain combinationsand arrangements of parts hereinafter described and particularly pointedyout in the claims, the advantages of which will be apparentrto thoseskilled in the art.

Two forms of the invention are shown in Figs. I and 2 respectively ofthe accompanying drawings.

Referring to Fig. l, the electron discharge tubes or devices 1 and 1a ofthe valve type having anodes 2 and 2*1 and theelectronemitting cathodes.3 and 3a respectively, are associated with a low or speech' frequencysource or circuit 4 and a high frequency source or circuit 5. Devices 1and 1* are unidirectionally conducting and have a non-V linear impedancecharacteristic in the conducting direction. Capacities 6, 7, 8 and 9 areintended to freely pass currents of the frequency existing in thecircuit but to offer a high impedance to currents'of voice frequencysuch as exist in circuit 4. Coils lO'and 11 on the contrary are designedto freely pass currents of the frequencies existing in circuit 4 but tooer a high-impedance to current of the frequency existing in circuit 5'.Alternating currents in circuit 4 will cause corresponding voltages tobe impressed upon the devices 1 and 1 .quency voltages due toalternating through the transformer 12, while alternatingcurrents incircuit 5 will cause corresponding electromotive forces to be 'impressedupon the devices 1 and 1 through the transformer 13. A transformer 14couples an output line 15 to the same branch of the circuit as contains,the secondary of transformer 13. y

Speech or low frequency waves acting in the circuit 4 cause correspondinvariations of potential directly across the evice 1 and across thedevice 1a through coils 10 and 11.

The high frequency current through the primary of the transformer'14willA thereby be caused to vary in amplitude, which willv produce injthe line 15` a modulated or varied high frequency current. Referring tothemodiied arrangement of Fig. 2, it will be noted that the lowfrecurrent in the circuit 4 are impressed simi arly and simultaneouslyon the devices 1 and 1 by means of two transformers 16 and 17. Thesecondaries of the transformers act as choke coils to prevent theVpassageof4 high fre-- quency currents, due to the impression ofvoltages on the secondary of transformer 13 by current in the circuit 5.Condensers 18, 19 and 20 are of such capacity as to highly impedecurrents of the fre uencies existing in the circuit 4. Capac1ty`20 maybe variable and if desired may be adjusted-so as to make the branch13-20-14 resonant to the high frequency current.

Owing to the action of devices 1 and 1 modulated high frequenc currentwill be produced in the output ine 15 when low` I and high frequencycurrents are produced in the circuits 4 and 5 respectively.

Devices land 1 are similarly related to 4 one of the circuits 4 and 5and oppositely related to the other thereof. The circuit to which theyare similarly related is in the present instance the circuit 4.

Novel features inherent in are defined in the appended claims.-

A What is-'claimed isz 1. Av modulating system comprising an electronicdischarge device normally having zero space current, an anode andla'cathode 106 therefor, means to impress a voltage of carrier frequencyto Ibe modulated, and means to impress a modulating frequency voltageacross said anode and cathode.

2.A modulating system comprising. a 110 the invention 10o p pair oftwo-electrode therrnionic discharge devices oppositely disposed withrespect. to a source of carrier waves to be modulated and a source withrespect to which said devices are in similar parallel relation forimpressing a low frequency modulating voltage across said electrodes.

3. A modulating system comprising high frequency source of waves to bemodulated, a low frequency source of modulating ducting space dischargepaths, said paths beingvsimilarly poled with respect to one of saidsources, path in which currents are induced by the other of saidsources, said discharge paths being connected in parallel between twooints 1n said path in which currents are induced, in such a'manner as.to respectively present opposite poles to their common, points ofconnection.

A modulating system comprising a pair of thermionic dlscharge devicesoppositely disposed with respect to a. high frequcncy source of wavestofbe:modulated,V`A V and a low frequency source of modulating waveswith respect to which said devices are similarly disposed.

6. A system comprising a pair of thermionic discharge devices disposedin parallel relation with respect to a low frequency source ofmodulating waves, an 'output circuit with respect to which said devicesare oppositely disposed, and a high frequency source of waves to bemodulated with respect to which said devices are also oppositelydisposed;

7. wave modifying system comprising a pair of thermionic dischargedevices, a source of waves to be modulated connected in parallelrelation with respect to but oppositely poled with respect to saiddevices,

and a second source of waves of a different characteristic similarlydisposed with respect to said devices, one of said sourcesv `comprisingcarrier waves and the other comprising vmodulating waves.

8. A wave modifying system lcomprising a pair of thermionic rectifyingdevices, an input source of low frequency waves, an

input source of high frequency waves, andan output path, said lnputsource of high y frequency waves and said output path being coupled tothe same path connecting said devices.

In witness whereof,y I hereunto subscribe \my name this 26th day ofAugust, A. D;

ALBERT L. FITCH.

